Adding a environment class to pass around state.

This makes it possible for telemetry to have multiple perf-directories in which page sets, measurements, benchmarks, etc are located. This is needed when a customer downstream of Chrome wants to use Chrome's perf suite and add more of their own.

BUG=
R=achuith@chromium.org, dtu@chromium.org, nduca@chromium.org

Review URL: https://codereview.chromium.org/178043004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253286 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253286